A Fully Integrated 11.2-mm2 a-IGZO EMG Front-End Circuit on Flexible Substrate Achieving Up to 41-dB SNR and 29-M $\Omega$ Input Impedance

A biopotential front-end (FE) circuit is designed and fabricated using amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs on flexible plastic substrate. Its input chopper provides both noise reduction and frequency division multiplexing among multiple FEs in an array. Measurements of the FE at chopping frequencies from 5 to 8 kHz show a gain in the range of 24.9-23.1 dB, bandwidth of 5.4-5.2 kHz, input noise in the EMG band ranging from 125 μVRMS to 31.4 μVRMS, and an input impedance of 29.6-23 MΩ. At different chopping frequencies, the SNR in the EMG band is respectively, 29, 32.3, 38, and 41 dB, enough to monitor muscle fiber conduction velocity. This is achieved in a total area of 11.2 mm
²
and with 1.3-mW power consumption. In-vivo recordings of EMG from the forearm of a person using the fabricated FE and standard gel electrodes have been performed. The measurements show EMG bursts with a maximum amplitude of 1.6 mV, which is within the physiological range for this muscle. The proposed circuit achieves an 8.9× reduction in size compared to previous FEs fabricated on flexible foil for EMG applications, enabling a spatial resolution in the order of a few millimeters, with great benefit for the diagnosis of neuromuscular disorders.